Non-fracturing restimulation of unconventional hydrocarbon containing formations to enhance production

ABSTRACT

There is provided system and methods for restimulating a hydrocarbon producing well using water and pressures below the closure pressure, which results in production rates approaching the initial production rate of the well. There is provided multiple restimulation techniques using water based fluids at or below the closure pressure of the well, which results in production rates approach that of the prior rate upon stimulation.

This application is a continuation of U.S. patent application Ser. No.15/962,973, filed Apr. 25, 2018, which claims under 35 U.S.C. §119(e)(1) the benefit of the filing date of U.S. provisional applicationSer. No. 62/489,932 filed Apr. 25, 2017, the entire disclosure of eachof which is incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present inventions relate to the enhanced recovery of naturalresources from within the earth; including systems, apparatus andmethods to increase the production of natural resources from existingproducing locations, minimizing the level of decline in production fromexisting production locations, and preferably increasing the level ofproduction from existing production locations. In particular, anembodiment of the present inventions, relates to the enhanced recoveryof hydrocarbons, e.g., crude oil and natural gas, from existing wellsfrom unconventional shale formations within the earth.

In the production of natural resources from formations within the eartha well or borehole is drilled into the earth to the location where thenatural resource is believed to be located. These natural resources maybe a hydrocarbon reservoir, containing natural gas, crude oil andcombinations of these; the natural resource may be fresh water; it maybe a heat source for geothermal energy; or it may be some other naturalresource that is located within the ground.

These resource-containing formations may be a few hundred feet, a fewthousand feet, or tens of thousands of feet below the surface of theearth, including under the floor of a body of water, e.g., below the seafloor. In addition to being at various depths within the earth, theseformations may cover areas of differing sizes, shapes and volumes.

Unfortunately, and generally, when a well is drilled into theseformations the natural resources rarely flow into the well at rates,durations and amounts that are economically viable. This problem occursfor several reasons, some of which are well understood, others of whichare not as well understood, and some of which may not yet be known.These problems can relate to the viscosity of the natural resource, theporosity of the formation, the geology of the formation, the formationpressures, and the perforations that place the production tubing in thewell in fluid communication with the formation, to name a few.

Typically, and by way of general illustration, in drilling a well aninitial borehole is made into the earth, e.g., the surface of land orseabed, and then subsequent and smaller diameter boreholes are drilledto extend the overall depth of the borehole. In this manner as theoverall borehole gets deeper its diameter becomes smaller; resulting inwhat can be envisioned as a telescoping assembly of holes with thelargest diameter hole being at the top of the borehole closest to thesurface of the earth.

Thus, by way of example, the starting phases of a subsea drill processmay be explained in general as follows. Once the drilling rig ispositioned on the surface of the water over the area where drilling isto take place, an initial borehole is made by drilling a 36″ hole in theearth to a depth of about 200-300 ft. below the seafloor. A 30″ casingis inserted into this initial borehole. This 30″ casing may also becalled a conductor. The 30″ conductor may or may not be cemented intoplace. During this drilling operation a riser is generally not used andthe cuttings from the borehole, e.g., the earth and other materialremoved from the borehole by the drilling activity are returned to theseafloor. Next, a 26″ diameter borehole is drilled within the 30″casing, extending the depth of the borehole to about 1,000-1,500 ft.This drilling operation may also be conducted without using a riser. A20″ casing is then inserted into the 30″ conductor and 26″ borehole.This 20″ casing is cemented into place. The 20″ casing has a wellheadsecured to it. (In other operations an additional smaller diameterborehole may be drilled, and a smaller diameter casing inserted intothat borehole with the wellhead being secured to that smaller diametercasing.) A BOP (blow out preventer) is then secured to a riser andlowered by the riser to the sea floor; where the BOP is secured to thewellhead. From this point forward all drilling activity in the boreholetakes place through the riser and the BOP.

It should be noted that riserless subsea drilling operations are alsocontemplated.

For a land based drill process, the steps are similar, although thelarge diameter tubulars, 30″-20″ are typically not used. Thus, andgenerally, there is a surface casing that is typically about 13⅜″diameter. This may extend from the surface, e.g., wellhead and BOP, todepths of tens of feet to hundreds of feet. One of the purposes of thesurface casing is to meet environmental concerns in protecting groundwater. The surface casing should have sufficiently large diameter toallow the drill string, product equipment such as ESPs and circulationmud to pass through. Below the casing one or more different diameterintermediate casings may be used. (It is understood that sections of aborehole may not be cased, which sections are referred to as open hole.)These can have diameters in the range of about 9″ to about 7″, althoughlarger and smaller sizes may be used, and can extend to depths ofthousands and tens of thousands of feet. Inside of the casing andextending from a pay zone, or production zone of the borehole up to andthrough the wellhead on the surface is the production tubing. There maybe a single production tubing or multiple production tubings in a singleborehole, with each of the production tubing endings being at differentdepths.

Typically, when completing a well, it is necessary to perform aperforation operation, and perform a hydraulic fracturing, or fracingoperation. In general, when a well has been drilled and casing, e.g., ametal pipe, is run to the prescribed depth, the casing is typicallycemented in place by pumping cement down and into the annular spacebetween the casing and the earth. (It is understood that many differentdown hole casing, open hole, and completion approaches may be used.) Thecasing, among other things, prevents the hole from collapsing and fluidsfrom flowing between permeable zones in the annulus. Thus, this casingforms a structural support for the well and a barrier to the earth.

While important for the structural integrity of the well, the casing andcement present a problem when they are in the production zone. Thus, inaddition to holding back the earth, they also prevent the hydrocarbonsfrom flowing into the well and from being recovered. Additionally, theformation itself may have been damaged by the drilling process, e.g., bythe pressure from the drilling mud, and this damaged area of theformation may form an additional barrier to the flow of hydrocarbonsinto the well. Similarly, in most situations where casing is not neededin the production area, e.g., open hole, the formation itself isgenerally tight, and more typically can be very tight, and thus, willnot permit the hydrocarbons to flow into the well. In some situations,the formation pressure is large enough that the hydrocarbons readilyflow into the well in an uncased, or open hole. Nevertheless, asformation pressure lessens a point will be reached where the formationitself shuts-off, or significantly reduces, the flow of hydrocarbonsinto the well. Also, such low formation pressure could have insufficientforce to flow fluid from the bottom of the borehole to the surface,requiring the use of artificial lift.

To address, in part, this problem of the flow of hydrocarbons (as wellas other resources, e.g., geothermal) into the well being blocked by thecasing, cement and the formation itself, openings, e.g., perforations,are made in the well in the area of the pay zone. Generally, aperforation is a small, about ¼″ to about 1″ or 2″ in diameter hole thatextends through the casing, cement and damaged formation and goes intothe formation. This hole creates a passage for the hydrocarbons to flowfrom the formation into the well. In a typical well, a large number ofthese holes are made through the casing and into the formation in thepay zone.

Generally, in a perforating operation a perforating tool or gun islowered into the borehole to the location where the production zone orpay zone is located. The perforating gun is a long, typically roundtool, that has a small enough diameter to fit into the casing or tubularand reach the area within the borehole where the production zone isbelieved to be. Once positioned in the production zone a series ofexplosive charges, e.g., shaped charges, are ignited. The hot gases andmolten metal from the explosion cut a hole, i.e., the perf orperforation, through the casing and into the formation. Theseexplosive-made perforations extend a few inches, e.g., 6″ to 18″, intothe formation.

The ability of, or ease with which, the natural resource can flow out ofthe formation and into the well or production tubing (into and out of,for example, in the case of engineered geothermal wells, and someadvanced recovery methods for hydrocarbon wells) can generally beunderstood as the fluid communication between the well and theformation. As this fluid communication is increased several enhancementsor benefits may be obtained: the volume or rate of flow (e.g., gallonsper minute) can increase; the distance within the formation out from thewell where the natural resources will flow into the well can be increase(e.g., the volume and area of the formation that can be drained by asingle well is increased, and it will thus take less total wells torecover the resources from an entire field); the time period when thewell is producing resources can be lengthened; the flow rate can bemaintained at a higher rate for a longer period of time; andcombinations of these and other efficiencies and benefits.

Fluid communication between the formation and the well can be greatlyincreased by the use of hydraulic fracturing techniques. The first usesof hydraulic fracturing date back to the late 1940s and early 1950s. Ingeneral, hydraulic fracturing treatments involve forcing fluids down thewell and into the formation, where the fluids enter the formation andcrack, e.g., force the layers of rock to break apart or fracture. Thesefractures create channels or flow paths that may have cross sections ofa few micron's, to a few millimeters, to several millimeters in size,and potentially larger. The fractures may also extend out from the wellin all directions for a few feet, several feet and tens of feet orfurther. It should be remembered that the longitudinal axis of the wellin the reservoir may not be vertical: it may be on an angle (eitherslopping up or down) or it may be horizontal. For example, in therecovery of shale gas and oil the wells are typically essentiallyhorizontal in the reservoir. The section of the well located within thereservoir, i.e., the section of the formation containing the naturalresources, can be called the pay zone.

Typical fluid volumes in the initial propped fracturing treatment of aformation in general can range from a few thousand to a few milliongallons. This initial hydraulic fracturing operation can have severalphases, each having different volumes of fluids, pressures and amountsof proppant. These initial propped fracturing treatments take placeduring the competition phase of the well, before or as it goes “on line”to become a producing well. Although in other types of completions thewells may only be hydraulically fractured and no proppant is used. Ingeneral, the objective of hydraulic fracturing is to create and enhancefluid communication between the wellbore and the hydrocarbons in theformation, e.g., the reservoir.

The fluids used to perform the initial hydraulic fracture, i.e., duringthe completion phase, can range from very simple, e.g., water, to verycomplex. Additionally, these fluids, e.g., fracing fluids or fracturingfluids, typically carry with them proppants; but not in all cases, e.g.,when acids are used to fracture carbonate formations. Proppants aresmall particles, e.g., grains of sand, aluminum shot, sintered bauxite,ceramic beads, resin coated sand or ceramics, that are flowed into thefractures and hold, e.g., “prop” or hold open the fractures when thepressure of the fracturing fluid is reduced and the fluid is removed toallow the resource, e.g., hydrocarbons, to flow into the well.

In this manner the proppants hold open the fractures, keeping thechannels open so that the hydrocarbons can more readily flow into thewell. Additionally, the fractures greatly increase the surface area fromwhich the hydrocarbons can flow into the well. Proppants may not beneeded, or generally may not be used when acids are used to create afrac and subsequent channel in a carbonate rich reservoir, where theacids dissolve part or all of the rock leaving an opening for theformation fluids to flow to the wellbore.

Typically fracturing fluids consist primarily of water but also haveother materials in them. The number of other materials, e.g., chemicaladditives used in a typical initial fracture treatment during completionvaries depending on the conditions of the specific wellbeing fractured.Generally, a typical fracture treatment will use from about 2 to about25 additives.

For both convention and unconventional (e.g., tight or shale formations)after the hydraulic fracturing and other completion operations the wellthen starts to produce hydrocarbons. This first, i.e., initialproduction, from the well can be greatly increased by hydraulicfracturing and other completion techniques. Unfortunately, however, forall wells, in all types of formations, this initial production begins todecline, in what is referred to as a decline curve. This drop in initialproduction can start about 1 month, about 3 months, about 6 months orabout 1 year into the life of the well. The decline curve can begradual, or it can be step. In situations where the decline curve isstep, the product can drop below levels that are economically viable(depending on the current hydrocarbon prices). The total production fromthe well, i.e., total amount of oil produced by the well over time, canbe greatly, and adversely effected by a step decline curve, and inparticular a step decline curve that manifests itself early in the lifeof the well.

The problem of such drops in initial production, and reduced totalproduction, from wells has been long standing. These problems haveresulted in the abandonment of many wells, leveling hundreds ofthousands of barrels of oil and cubic feet of natural gas unrecoveredand essentially unrecoverable. In particular, in unconventional wells.the art has been looking for ways to forestall the onset of the declinecurve, to slow the rate of decline curve, and to increase the rate ofproduction and the total product from a well.

Generally, before the present inventions, the art has addressed thedecline curve problem with greater complexity, both chemically andthrough well design, and through brute force. Restimulation hydraulicfracturing operations can pump millions of gallons of water into a wellat pressures far above the closure pressure of the formation in attemptsto further break the rock and free up the hydrocarbons. Secondary andtertiary operations are employed with the need for injection wells,sweep wells, steam, etc. These prior art approaches generally have onething in common, they subject the well and the formation to more andgreater forces and harsher conditions to free up the remaininghydrocarbons.

Related Art and Terminology

As used herein, unless specified otherwise, the terms “hydrocarbonexploration and production”, “exploration and production activities”,“E&P”, and “E&P activities”, and similar such terms are to be giventheir broadest possible meaning, and include surveying, geologicalanalysis, well planning, reservoir planning, reservoir management,drilling a well, workover and completion activities, hydrocarbonproduction, flowing of hydrocarbons from a well, collection ofhydrocarbons, secondary and tertiary recovery from a well, themanagement of flowing hydrocarbons from a well, and any other upstreamactivities.

As used herein, unless specified otherwise, the term “earth” should begiven its broadest possible meaning, and includes, the ground, allnatural materials, such as rocks, and artificial materials, such asconcrete, that are or may be found in the ground.

As used herein, unless specified otherwise “offshore” and “offshoredrilling activities” and similar such terms are used in their broadestsense and would include drilling activities on, or in, any body ofwater, whether fresh or salt water, whether manmade or naturallyoccurring, such as for example rivers, lakes, canals, inland seas,oceans, seas, such as the North Sea, bays and gulfs, such as the Gulf ofMexico. As used herein, unless specified otherwise the term “offshoredrilling rig” is to be given its broadest possible meaning and wouldinclude fixed towers, tenders, platforms, barges, jack-ups, floatingplatforms, drill ships, dynamically positioned drill ships,semi-submersibles and dynamically positioned semi-submersibles. As usedherein, unless specified otherwise the term “seafloor” is to be givenits broadest possible meaning and would include any surface of the earththat lies under, or is at the bottom of, any body of water, whetherfresh or salt water, whether manmade or naturally occurring.

As used herein, unless specified otherwise, the term “borehole” shouldbe given it broadest possible meaning and includes any opening that iscreated in the earth that is substantially longer than it is wide, suchas a well, a well bore, a well hole, a micro hole, a slimhole and otherterms commonly used or known in the arts to define these types of narrowlong passages. Wells would further include exploratory, production,abandoned, reentered, reworked, and injection wells. They would includeboth cased and uncased wells, and sections of those wells. Uncasedwells, or section of wells, also are called open holes, or open holesections. Boreholes may further have segments or sections that havedifferent orientations, they may have straight sections and arcuatesections and combinations thereof. Thus, as used herein unless expresslyprovided otherwise, the “bottom” of a borehole, the “bottom surface” ofthe borehole and similar terms refer to the end of the borehole, i.e.,that portion of the borehole furthest along the path of the boreholefrom the borehole's opening, the surface of the earth, or the borehole'sbeginning. The terms “side” and “wall” of a borehole should to be giventheir broadest possible meaning and include the longitudinal surfaces ofthe borehole, whether or not casing or a liner is present, as such,these terms would include the sides of an open borehole or the sides ofthe casing that has been positioned within a borehole. Boreholes may bemade up of a single passage, multiple passages, connected passages,(e.g., branched configuration, fishboned configuration, or combconfiguration), and combinations and variations thereof.

As used herein, unless specified otherwise, the term “advancing aborehole”, “drilling a well”, and similar such terms should be giventheir broadest possible meaning and include increasing the length of theborehole. Thus, by advancing a borehole, provided the orientation is nothorizontal and is downward, e.g., less than 90°, the depth of theborehole may also be increased.

Boreholes are generally formed and advanced by using mechanical drillingequipment having a rotating drilling tool, e.g., a bit. For example, andin general, when creating a borehole in the earth, a drilling bit isextending to and into the earth and rotated to create a hole in theearth. To perform the drilling operation the bit must be forced againstthe material to be removed with a sufficient force to exceed the shearstrength, compressive strength or combinations thereof, of thatmaterial. The material that is cut from the earth is generally known ascuttings, e.g., waste, which may be chips of rock, dust, rock fibers andother types of materials and structures that may be created by the bit'sinteractions with the earth. These cuttings are typically removed fromthe borehole by the use of fluids, which fluids can be liquids, foams orgases, or other materials know to the art.

The true vertical depth (“TVD”) of a borehole is the distance from thetop or surface of the borehole to the depth at which the bottom of theborehole is located, measured along a straight vertical line. Themeasured depth (“MD”) of a borehole is the distance as measured alongthe actual path of the borehole from the top or surface to the bottom.As used herein unless specified otherwise the term depth of a boreholewill refer to MD. In general, a point of reference may be used for thetop of the borehole, such as the rotary table, drill floor, well head orinitial opening or surface of the structure in which the borehole isplaced.

As used herein, unless specified otherwise, the term “drill pipe” is tobe given its broadest possible meaning and includes all forms of pipeused for drilling activities; and refers to a single section or piece ofpipe. As used herein the terms “stand of drill pipe,” “drill pipestand,” “stand of pipe,” “stand” and similar type terms should be giventheir broadest possible meaning and include two, three or four sectionsof drill pipe that have been connected, e.g., joined together, typicallyby joints having threaded connections. As used herein the terms “drillstring,” “string,” “string of drill pipe,” string of pipe” and similartype terms should be given their broadest definition and would include astand or stands joined together for the purpose of being employed in aborehole. Thus, a drill string could include many stands and manyhundreds of sections of drill pipe.

As used herein, unless specified otherwise, the terms “workover,”“completion” and “workover and completion” and similar such terms shouldbe given their broadest possible meanings and would include activitiesthat take place at or near the completion of drilling a well, activitiesthat take place at or the near the commencement of production from thewell, activities that take place on the well when the well is aproducing or operating well, activities that take place to reopen orreenter an abandoned or plugged well or branch of a well, and would alsoinclude for example, perforating, cementing, acidizing, fracturing,pressure testing, the removal of well debris, removal of plugs,insertion or replacement of production tubing, forming windows in casingto drill or complete lateral or branch wellbores, cutting and millingoperations in general, insertion of screens, stimulating, cleaning,testing, analyzing and other such activities.

As used herein, unless specified otherwise, the terms “formation,”“reservoir,” “pay zone,” and similar terms, are to be given theirbroadest possible meanings and would include all locations, areas, andgeological features within the earth that contain, may contain, or arebelieved to contain, hydrocarbons.

As used herein, unless specified otherwise, the terms “field,” “oilfield” and similar terms, are to be given their broadest possiblemeanings, and would include any area of land, sea floor, or water thatis loosely or directly associated with a formation, and moreparticularly with a resource containing formation, thus, a field mayhave one or more exploratory and producing wells associated with it, afield may have one or more governmental body or private resource leasesassociated with it, and one or more field(s) may be directly associatedwith a resource containing formation.

As used herein, unless specified otherwise, the terms “conventionalgas”, “conventional oil”, “conventional”, “conventional production” andsimilar such terms are to be given their broadest possible meaning andinclude hydrocarbons, e.g., gas and oil, that are trapped in structuresin the earth. Generally, in these conventional formations thehydrocarbons have migrated in permeable, or semi-permeable formations toa trap, or area where they are accumulated. Typically, in conventionalformations a non-porous layer is above, or encompassing the area ofaccumulated hydrocarbons, in essence trapping the hydrocarbonaccumulation. Conventional reservoirs have been historically the sourcesof the vast majority of hydrocarbons produced. As used herein, unlessspecified otherwise, the terms “unconventional gas”, “unconventionaloil”, “unconventional”, “unconventional production” and similar suchterms are to be given their broadest possible meaning and includeshydrocarbons that are held in impermeable rock, and which have notmigrated to traps or areas of accumulation.

As used herein, unless stated otherwise, room temperature is 25° C. And,standard temperature and pressure is 25° C. and 1 atmosphere. As usedherein, unless stated otherwise, generally, the term “about” is meant toencompass a variance or range of ±10%, the experimental or instrumenterror associated with obtaining the stated value, and preferably thelarger of these.

This Background of the Invention section is intended to introducevarious aspects of the art, which may be associated with embodiments ofthe present inventions. Thus, the forgoing discussion in this sectionprovides a framework for better understanding the present inventions,and is not to be viewed as an admission of prior art.

SUMMARY

There has been a long-standing, expanding and unmet need, for improvedways to obtain resources, and in particular, hydrocarbon resources fromthe earth. Thus, there exists a long felt, increasing and unfulfilledneed for, among other things, systems and methods for extending theuseful life of wells, reducing the rate of decline in a well, andincreasing the total production obtained from a well. The presentinventions, among other things, solve these needs by providing thearticles of manufacture, devices and processes taught, and disclosedherein.

There is provided a method of reducing the decline curve in productionrate for an existing well in a formation, the method including:identifying a producing well that has a production rate, wherein theproduction rate is at least 20% below an initial production rate for thewell; and wherein the well has a closure pressure; pumping arestimulation fluid into the well at a predetermined flow rate andpredetermined pressure, wherein the closure pressure of the well is notexceeded; whereby, the production rate of the well is increased by notless than 50%.

There is further provided these methods including on or more of thefollowing features: wherein there is no perceivable fracturing of theformation; wherein there is no fracturing of the formation; wherein theproduction rate of the well is increased by not less than 100%; whereinthe production rate of the well is increased by not less than 75%;wherein the restimulation fluid consists of water; wherein therestimulation fluid consists essentially of water; wherein therestimulation fluid comprises water; wherein the restimulation fluid isfree from additives selected from the group consisting of solvents,biocides, and scale inhibitors; and, wherein the restimulation fluid isfree from additives selected from the group consisting of thickeningagents, surfactants, and scale inhibitors; wherein the restimulationfluid comprises used fracturing fluid.

Moreover, there is provided these methods including on or more of thefollowing features: wherein the production rate of the well is increasedby at least 100%; and wherein the production rate of the well isincreased by at least 75%.

Yet additionally, there is provided a method of reducing the declinecurve in production rate for an existing well in a formation, the methodincluding: identifying a producing well that has a production rate,wherein the production rate is at least 20% below an initial productionrate for the well; and wherein the well has a closure pressure; pumpinga restimulation fluid into the well at a predetermined flow rate andpredetermined pressure, wherein the closure pressure of the well is notexceeded; whereby, the production rate of the well is increased by notless than 50%.

Still further there is provided a method for increasing a productionrate of the production of hydrocarbons from an existing well in aformation, the method including: pumping a restimulation fluid into thewell at a predetermined flow rate and predetermined pressure, wherein astasis is achieved that is at or below the closure pressure of the well;maintaining the well at the stasis; and, whereby, existing fractures areopened without the formation of new fractures.

Additionally, there is provided these methods having one or more of thefollowing features: whereby the production rate of the well is increasedby 5%; whereby the production rate of the well is increased by 10%;whereby the production rate of the well is increased by 15%; whereby theproduction rate of the well is increased by 20%; and whereby theproduction rate of the well is increased and the increase is not lessthan a 20% increase, not less than a 40% increase, not less than a 50%,not less than a 100% increase in product rate just prior to therestimulation.

Still further, there is provided these methods having one or more of thefollowing features: wherein the stasis is at just below the closurepressure; wherein the stasis is at about 90% of the closure pressure;wherein the stasis is at about 85% of the closure pressure; wherein thestasis is maintained for 30 minutes; wherein the stasis is maintainedfor 2 hours; wherein the stasis is maintained from about 15 minutes toabout 2 hours; wherein the stasis is maintained from about 15 minutes toabout 1 hour; wherein the stasis is maintained from about 30 minutes toabout 3 hours; and wherein the stasis is less than about 2 hour, andwherein the stasis is less than 3 hours.

In addition, there is provided a method of stimulating a well havingexisting fractures, wherein the existing fractures include inducedfractures, naturally occurring fractures or both of these types offractures, and a production rate of hydrocarbons, by repressurization,the method including: pumping a repressurization fluid into the well,thereby establishing and maintaining a stasis; wherein at the stasisexisting fractures are opened and pore surface are wetted with therepressurization fluid; wherein at the stasis no new fractures andcreated; and, whereby, the production rate of the well is increased.

There is provided a method of increasing the total product ofhydrocarbons from an existing well, by performing multiplerestimulations of the well and thereby repeatedly reducing the declinecurve in production rate for the, the method including: (a) performing afirst restimulation comprising the steps of: identifying a producingwell that has a production rate, wherein the production rate is at least20% below an initial production rate for the well; and wherein the wellhas a closure pressure; pumping a restimulation fluid into the well at apredetermined flow rate and predetermined pressure, for a predeterminedtime to provide a status time, the status time comprising a time ofabout 30 minutes to about 3 hours, wherein during the status time theclosure pressure of the well is not exceeded; and, thereby providing arestimulated well, wherein the production rate increased by not lessthan 20% to provide a first restimulated product rate; and (b)performing a second restimulation comprising the steps of: determiningthat a later production rate of the restimulated well, is at least 20%below the first restimulated production rate; and wherein therestimulated well has a later closure pressure, wherein the laterclosure pressure can be the same or different than the closure pressure;pumping a restimulation fluid into the well at a second predeterminedflow rate and a second predetermined pressure, for a secondpredetermined time, wherein the second rate, time and pressures can bethe same or different than the rate, time and pressures of step b. II.,to provide a second status time, wherein the second status timecomprising a time of about 30 minutes to about 3 hours, wherein duringthe second status time the later closure pressure of the well is notexceeded; whereby, the later production rate of the well is increased bynot less than 20% to provide a later restimulated product rate.

Moreover, there provided these methods having one or more of thefollowing features: wherein the restimulation steps are repeated aplurality of times over the life of a well, wherein steps (a) and (b)are repeated at least once; and wherein step (b) is repeated a pluralityof times.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a chart showing increased rate of production for a wellrestimulated in accordance with an embodiment of the present inventions.

FIG. 2 is a cross section schematic of an embodiment of a restimulationsite in accordance with the present inventions.

FIGS. 3A to D are cross sectional and schematic representations offormation properties, that relate to the embodiments of the presentinventions.

FIG. 4 is a schematic showing a type of contact angle measurement, thatrelates to embodiments in accordance with the present inventions.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present inventions generally relate to systems, methods andoperations to enhance the recovery of natural resources from the earth,by the use of restimulation operations.

In general, in an embodiment of the present restimulation operation afluid, preferably a liquid, is forced into a resource containing area orzone of the earth. The flow rate and pressure of the fluid is controlledin a predetermine manner to reopen, reconfigure, or separate priorfractures (both natural and man-made) while minimizing, and preferably,not causing any additional fracturing or damage to the rock.

Although the majority of this specification focusses on embodiments ofrestimulation operations for unconventional hydrocarbon (e.g., shale oiland natural gas) containing formations and reservoirs, it should beunderstood that this is only by way of a preferred embodiment.Embodiments of the present restimulation operations may findapplications and provide benefits in conventional wells and formations,in other types of hydrocarbon containing formations, on land and subsea,and geothermal applications, as well as, in the extraction of ores, gemsand minerals from the earth.

Generally, in an embodiment of the restimulation operation, an existingproducing oil well in an unconventional shale formation is selected.Typically, during completion, the well was hydraulically fractured withat least about 10,000 gallons (gals) of fracturing fluid, primarilywater, at least about 100,000 gals, at least about 1,000,000 gals ofwater, at least about 3,000,000 gals of water and more, larger andsmaller amounts of fluid may also be used. The fracturing fluidtypically contained from about 1 pound (lb) to about 15 lbs of proppantper gallon, and all amounts within this range, although larger andsmaller amounts of proppant, and different amounts with differentstages, may be used. The pressure of the fracturing fluid duringhydraulic fracturing can be greater than 2,000 psi, greater than 5,000psi, greater than 10,000 psi and greater than 12,000 psi, from about2,000 psi to about 12,000 psie, and all pressures within these ranges.Typically, during the initial hydraulic fracturing, the pressure in theformation is increased to the point where the rock is broken andfractured, the pressure may than be reduced (or maintained at about thispoint) as additional fluid is pumped into the formation and the proppantis carried with it. The pressure will then be reduced and the formationwill close in with the proppant keeping some of the fractures open,i.e., propping them open, to permit hydrocarbons to flow from theformation into the well and ultimately to the surface. This pressure,where the formation after being fractured closes back in, i.e., the“closure pressure,” is a well know feature of a well, and typically isdocumented, known or at least inferentially understood for eachproducing well that has been hydraulically fractured. If it is notknown, or the information was lost, it can readily be determined again.

After about 6 months of production (sooner in some instances and longerin others) the decline curve starts to appear for the well. The amountof oil or natural gas that was first produced (“initial production”)after the initial hydraulic fracturing, or stimulation, begins todecrease rapidly.

Turning to FIG. 1 there is a chart 100 showing the production rate of anunconventional shale well over time. The y-axis 102 represents thehydrocarbon production rate for the well (in either thousands of cubicfeet of natural gas per day, or barrels of oil per day), with theproduction rate increasing in the direction of the arrow on axis 102.The x-axis 103 represent time after the well goes on line in months.When the well first goes on line, i.e., starts producing hydrocarbons,this will be the time of the highest rate of production, which is theinitial production 101. Over time the production rate of the well willdecrease, e.g., a decline cure, which is shown by typical productioncurve 104. Depending on conditions, over 30%, over 40% and over 50%,from about 30% to about 50%, and all values within these ranges or alongcurve 104, of the initial production rate of an unconventional shalewell can be lost in the first 6 to 18 months of production. Althoughsteeper and shallower decline curves may also occur.

In an embodiment of the present invention, at a point in time along thedecline curve the well is restimulated, preferably using a restimulationfluid that is preferably essentially only water, and preferably onlywater. By “essentially” only water, it is meant that there are nochemicals or other materials added to the water the purpose offunctionality and that the water is at least 98% pure. Biocides andslimocides can be added to the water. Other chemicals and additives maybe added to the water for other purposes. However, it has surprisingbeen discovered that restimulation of a well with water, without the aidof chemical additives, can have the benefit of significantly reversingthe decline in the production rate of a well. The restimulation ispumped back into the well under pressure and flow rates that preferablydo not break the rock, and that are at or below the closure pressure ofthe formation. Most preferably just below the closure pressure, e.g.,from about 65% to about 97% of the closure pressure, from about 90% to98% of the closure pressure, about 95% of the closure pressure, about90% of the closure pressure, about 80% of the closure pressure and about70% of the closure pressure, and all values within these ranges.

Thus, turning to FIG. 1 a first restimulation operation 120 of thepresent invention was conducted, about 18 months into the life of thewell. Water was forced into the well at just below the closure pressureof the well, when the pressure was reduced and the well returned toproduction. The production rate 105 of the well, after the firstrestimulation operation 120, increased to about 80% of its initialproduction. This first restimulation 120 production rate, however maysee a decline cure 105, as shown in FIG. 1 . At a point alone thisdecline curve 105 the well may have a second restimulation operation 121conducted. This restimulation operation 121 again uses essentially onlywater and is kept at pressures just below the closure pressures. Thesecond restimulation operation 121 greatly increases the production rateproviding a new production curve or decline curve 106. This cycle ofdecline and restimulation can be repeated, as shown in the thirdrestimulation 122 and production rate increase and decline curve 107,and can be further repeated over time 123.

Thus, it can be seen that by restimulation with just water as therestimulation fluid, at pressures just below the closure pressure theproduction rate of the well can be increased. It is contemplated thatfor some wells the production rate can be increased to about 100% of theinitial production rate (as well as, initial rate after priorrestimulation, when multiple restimulations are used), to at least about95% of the initial production rate, to at least about 90% of the initialproduction rate, and to at least about 50% of the initial productionrate, from about 45% to about 100% of the initial product rate, fromabout 50% to about 75% of the initial product rate, as well as allvalues within these ranges. In the case of earlier restimulations, thesepercentages of “initial” recovery would be the last prior productionrate after a restimulation, e.g., rate after second restimulation, rateafter third restimulation, etc. (see FIG. 1 showing a percentage ofrecovery of rate after prior restimulation).

Additionally, the total production from the well can be increasedthrough the use of the present restimulation operations. Thus, asillustrated in FIG. 1 the area 130 between the restimulation productioncurves 105, 106, 107, etc., and the typical production curve 104,represents additional total production (additional total barrels of oilor total cubic feet of gas) that is recovered. Thus, for example, usingthe restimulation techniques of the present inventions it iscontemplated that the total recovery of a well can be increased by atleast about 5%, at least about 10%, at least about 30% and at leastabout 50% or more, from about 5% to about 20%, from about 5% to about50%, from about 5% to about 10%, from about 7% to about 25%, and, aswell as, all values within these ranges.

While percentage reductions were show in the chart of FIG. 1 for ease ofcomparison and illustration purposes. The production rates for shale oilfield wells and the resultant increase in production rate, or reductionin the rate of decline, can result in the recovery of significantamounts of hydrocarbons.

Thus, reported values for initial production rates for a typical well invarious shale fields is show in Table 1. The percentage improvements,decrease in decline rate, and increase in production rate, forembodiments of the present inventions, are applicable to the values ofTable 1, as well as larger, smaller and other production rates in thosegeneral ranges.

TABLE 1 New-well oil New-well gas production per rig production per rigbarrels/day thousand cubic feet/day August September August SeptemberRegion 2016 2016 change 2016 2016 change Bakken 857 875 18 1,149 1,18940 Eagle 1,076 1,089 13 3,194 3,232 38 Ford Haynes- 31 31 — 5,573 5,63966 ville Marcellus 69 69 — 11,353 11,503 150 Niobrara 961 982 21 3,0043,080 76 Permian 520 522 2 895 895 — Utica 351 360 9 7,547 7,659 112Rig- 560 578 18 2,859 2,767 (92) weighted average

In FIG. 2 , the is shown a cross sectional of a well in a formation anda restimulation system for preforming a restimulation operation. Therestimulation site 200 has a producing well 220 that extends below thesurface 202 of the earth 201 in a formation pay zone 212. Duringcompletion of the well 220 the bore hole 208 was perforated, e.g., 209,and stimulated by hydraulic fracturing with proppant. The area offracture or rock breakage is shown by dashed line 210, and the proppedarea, the area where the proppant was retained and holds the fracturesopen is shown by dashed line 211. A pump truck 203 (more than one may beused or required) has low pressure water line 205 feeding into thepumps. The water line 205 is connected to a source of water 204 (in thepreferred embodiment essentially water, and only water, or in otherembodiments, other restimulation fluids can be used). The pump truck hashigh pressure water line 206 that is feed into a BOP on the well held207.

Because lower pressures are used, e.g., pressures below the close offpressure, preferably packers and special tools are not required and arenot used for the restimulation. In the embodiment, the water is pumped(e.g., by truck 203 through line 206 into the well bore 208) into theformation pay zone 212, (e.g., the propped zone 211, the breakage zone210, and both) through the perforations, e.g., 209, at a pressure andflow rate sufficient to maintain the desired restimulation pressure,which is below the closure pressure of the pay zone 212.

Although not being bound or limited by the present theory, to advancethis important art, and explain the surprising and significate benefitsobtained by the present inventions, it is theorized that by using thislower pressure, and minimizing or avoiding additional damage to theformation, micro-fractures, closed or occluded fractures, and the like,may be reopened, that the fracture network may be reconfigured, orotherwise rearrangement, and all of these. In this manner, it is furthertheorized that additional surface area is provided, different surfacearea is provided, and both; and that this surface area provides for theproduction of additional hydrocarbons at increased rates of production.

Thus, further explaining the present theory, hydraulic fracturingcreates or provides in the formation a hydrocarbon transmission systemto open and network vast plated (planar) pore reserves of combined phasegaseous and long-chain hydrocarbon situated throughout the rock bypaning (window pane) systems of porous and permeable materialpredominately between least-stress planes of geological interface.Near-wellbore, and more specifically the near-fracture stress regimesare changed dramatically as rock is dilated and material is injectedfrom pressure pumping. The injected material proppant separating theplated geology expose pore reserves to order of magnitude changes inpermeability, yielding a transmission system and communication networkto the wellbore and then to surface. The more contact betweenpore-reserves and permeable-proppant, the better. This contact isbelieve to be increased by the present restimulation embodiments. Turingto FIG. 3 , and (a) through (s), as the hydrocarbons are removed fromthe formation, along or via the various fracture paths, especially overprolonged periods, mechanical deformation in the rock occurs, resultingfrom substantial displacement of fluid and gas volumes from the rock. Ashydrocarbon volumes are produced, thus displacing hydrocarbon volumesfrom the formation, structural support of the formation issimultaneously displaced, creating an environment of constant, creepingreorganization of material structure altering the geometry of the of therock-proppant interface and the stress regime of the rock, therebycreating more fractures along secondary stress planes, etc., and thusunlocking more potential, but yet uncontacted, surface area containingpore-reserve bearing geology. “Natural” secondary fracture systems arecreated as a result of production volume displacement through theinduced primary fracture system. The creep-induced increase in surfacearea of the rock at the proppant-geological bed boundary consequentlydepletes throughout the production cycle and also corresponds to reducedconductivity throughout the proppant layers as overburden cooperateswith changing reservoir conditions to do damaging work on ourtransmission infrastructure, something analogous to buckling in pipe andrestriction in nozzle, and our communication networks break down. It istheorized that the repressurization of the formation, throughembodiments of the present restimulation techniques, provides for arearrangement of sort, that enables the potential surface area from thenatural fractures that were created over time to be utilized forproduction.

Additionally, it is theorized that, as show in FIG. 4 , that the waterdisplaces hydrocarbon from the pore as the wettability preference of therock change instantaneously. In this manner, the repressurization fluidcan readily reach and reopen closed porosity and unused porosity withoutthe need to have large pressures, as the capillaries are drawing thewater into replace any hydrocarbon that may be present. Thus, theseclosed and unused porosity can be reopened at pressures at or below thefracture pressure.

Prior to the present inventions, it was generally known that a wellcould be repressurized to prevent fracturing fluid, from the fracturingof an adjacent well, from damaging the well, or being wasted by enteringinto areas of the formation that have already been fractured. Generally,however, the pressures used for these repressurizations, i.e., aprophylactic repressurization, were based upon the pressures of thefracturing fluid, the distance between the wells and other facts. Theseprophylactic repressurizations protected the well, they did not, and donot, restimulate it. Embodiments of the present inventions greatly arescientifically different from, and greatly improve upon these priorprophylactic repressurizations. The present inventions focus onproviding a pressure that is at, or just below the fracture pressure, inthis manner reopening existing fractures and expose greater surface areto those fractures for increased drainage and production. In this mannerone, two, all nearby wells, or an entire field can be restimulated asnew wells are fractured.

Embodiments of the present inventions restimulated wells, and provideincreased rates of hydrocarbon production, without creating additionalfractures in the formation of the pay zone, that is adjacent the wellbore.

The following examples are provided to illustrate various embodiments ofthe present restimulation operations. These examples are forillustrative purposes, may be prophetic, and should not be viewed as,and do not otherwise limit the scope of the present inventions.

EXAMPLES Example 1

Method for the protection and enhancement of stimulation of fragilefracture network systems in existing wells.

To dilate existing plumbing of an old well repressurization fluid ispumped into the old well at initial pumping rates between 1-5 bbl/min(barrel oil per minute, 1 bbl/min is equal to 158.99 L/min, 42gals/min), recognizing that large and smaller initial pumping rates maybe used or needed. During initial pumping the surface pressure iscarefully monitored, an in particular carefully monitored as the surfacepressure begins to approach the opening pressure of the old well. As theopening pressure of the old well is approached, the rates of the pumpswill be lowered, lowered below their initial pump rates, and further tomake certain so as not to exceed fracture pressure. Thus, in controllingthe pumping rate and pressure, it is understood that the fluid productbeing pumped into the well, forms a solid column of fluid or solidcolumn of gas. In an embodiment of this example, the fluid being pumpedis water having a purity of at least 98% and having no functionalchemicals or additives in it. In another embodiment of this example, thefluid being pumped is water with biocides, scale inhibitors added to it.In another embodiment, the fluid is used frac fluid that has beencleaned to remove particulates that could damage the well, equipment orboth.

Example 2

Prior to the fracturing of a new well, in a field, having severalexisting wells, production in the existing wells that are directlyadjacent to the new is ceased. Once production has stopped the existingadjacent wells are cleaned out to remove bridges or other restrictionsin those wells that could affect flow rate and production. As thefracturing of the new well begins, and more preferably, prior to thefirst stage (e.g., the pad) of the fracturing job on the new well, therepressurizing fluid is pumped into the existing directly adjacent wellsto increase the pressure in those wells.

Typically from about 500 to 2,500 bbl. (greater amounts can be used orneeded, e.g., 5,000 bbl, 7,500 bbl and more) are pumped into each of thedirectly adjacent existing wells. The fluid is pumped into each well andsurface pressure for each well is closely monitored to be maintained at,or just below, fracture pressure for each of the existing wells. Thus, asituation of stasis should be obtained for each of the existing wells.The pressures are then maintained throughout the fracturing of the newwell, and maintained through all stages of the frac job of the new well.The pressures in the existing wells should then be maintained for a timeafter the frac job has been complete (e.g., after the last high pressurestage of the frac job). Thus, stasis in the existing wells, at, or justbelow, the fracture pressure for the existing wells should be maintainedfor about 15 minutes, about 30 minutes, about 1 hour, from about 10minutes to about 2 hours, from about 30 minutes to about 2 hours, aswell as all times within these ranges, and longer or shorter times.

It should be noted that the pressure at stasis for each of the existingwells may be different as each of the existing wells may have adifferent fracture pressure.

Example 3

The repressurization operation of Example 2 is performed on existingwells in the field that are nearby the new well, as well as, to theexisting wells that are directly adjacent to the new well.

Example 4

In an existing field, there are several new well that define a generalarea of the field. The repressurization operation of Example 2 isperformed on all existing wells in that area.

Example 5

The repressurization fluid is water based, preferably water, or morepreferably essentially only water. It can also be other downhole fluids,including frac fluids, and waste fluids (provided that they aresufficiently free from particles and debris to not damage the well). Fora preferred embodiment of the present inventions no proppant of any sizeis present in the repressurization fluid, or used in the restimulationoperations. The repressurization fluids may also have additives, orcontain and include chemicals, biologics, nano-particles, as well as,other downhole materials, presently know to the art or later developed.These additives would include, such materials as thickening agents,surfactants (which may be conventional and/or nano-type surfactantscontaining various solvents, any chemical (we need to be broad here),biocides, scale inhibitors, and any assortment of chemical productswhich may be advantageous to the fluid as known to those knowledgeablein the art of stimulation.

Example 6

Preferably, the injection process, i.e., the repressurization of theexisting well, will be such that the pressure stays below parting (e.g.,fracture) pressure and does not open new fracture systems. In someembodiments, for some wells, however, the ability to exceed partingpressure can be tolerated for very short periods of time withoutsignificant adverse consequences, provided the pump rate, and thus thepressures are dropped back down quickly, e.g., less than about 30minutes, less than about 15 minutes, and less than about 10 minute, andfrom about 5 minutes to about 1 hour, and from about 10 minutes to about40 minutes, from about 10 minutes to about 1.2 hours, as well as, allvalues within these ranges and longer and shorter time periods. In wellswhere the precise closure pressure is not known, diagnostics can beperformed to establish fracture closure pressure. (Fracture pressure,fracture closure pressure, parting pressure, all refer to the samegeneral property of the formation, which is that pressure at, or justbelow that, at which new fractures in the rock will be made.) Althoughthere may be general knowledge of the fracture closure pressure for thefield or even the area of the field where the existing well is located,evaluations using techniques of pumping fluid at increasing rates toachieve fracture initiation followed by shut down to observer fractureclosure can be used. These evaluative techniques include step-ratetests, stress tests, and Diagnostic Fracture Injection Testing (DFIT),as well as, other tests known or later developed by the art.

It is noted that there is no requirement to provide or address thetheory underlying the novel and groundbreaking production rates,performance or other beneficial features and properties that are thesubject of, or associated with, embodiments of the present inventions.Nevertheless, various theories are provided in this specification tofurther advance the art in this important area, and in particular in theimportant area of hydrocarbon exploration and production. These theoriesput forth in this specification, and unless expressly stated otherwise,in no way limit, restrict or narrow the scope of protection to beafforded the claimed inventions. These theories many not be required orpracticed to utilize the present inventions. It is further understoodthat the present inventions may lead to new, and heretofore unknowntheories to explain the conductivities, fractures, drainages, resourceproduction, and function-features of embodiments of the methods,articles, materials, devices and system of the present inventions; andsuch later developed theories shall not limit the scope of protectionafforded the present inventions.

The various embodiments of restimulation operations set forth in thisspecification may be used for various oil and gas field operations,other mineral and resource recovery fields, as well as other activitiesand in other fields. Additionally, these embodiments, for example, maybe used with: oil and gas field systems, operations or activities thatmay be developed in the future; and with existing oil and gas fieldsystems, operations or activities which may be modified, in-part, basedon the teachings of this specification. Further, the various embodimentsset forth in this specification may be used with each other in differentand various combinations. Thus, for example, the configurations providedin the various embodiments of this specification may be used with eachother; and the scope of protection afforded the present inventionsshould not be limited to a particular embodiment, configuration orarrangement that is set forth in a particular embodiment, example, or inan embodiment in a particular Figure.

The invention may be embodied in other forms than those specificallydisclosed herein without departing from its spirit or essentialcharacteristics. The described embodiments are to be considered in allrespects only as illustrative and not restrictive.

What is claimed:
 1. A method of increasing a total production ofhydrocarbons from an existing well in a formation, over a predeterminedperiod of time, the method comprising: a. pumping a restimulation fluidinto the well at a predetermined flow rate and predetermined pressure,wherein a stasis is achieved that is at or below the closure pressure ofthe well; b. maintaining the well at the stasis for a predeterminedperiod of time; c. wherein, existing fractures are opened during thestasis; and, d. whereby the total production of hydrocarbons from thewell is increased, compared to a first total product for the well priorto restimulation, by at least about 10%; e. wherein the stasis is atabout 85% to 98% of the closure pressure.
 2. A method of increasing atotal production of hydrocarbons from an existing well in a formation,over a predetermined period of time, the method comprising: a. pumping arestimulation fluid into the well at a predetermined flow rate andpredetermined pressure, wherein a stasis is achieved that is at or belowthe closure pressure of the well; b. maintaining the well at the stasisfor a predetermined period of time; c. wherein, existing fractures areopened during the stasis; and, d. whereby the total production ofhydrocarbons from the well is increased, compared to a first totalproduct for the well prior to restimulation, by at least about 10%; e.wherein the stasis is at about 65% to about 85% of the closure pressure.3. A method of increasing a total production of hydrocarbons from anexisting well in a formation, over a predetermined period of time, themethod comprising: a. pumping a restimulation fluid into the well at apredetermined flow rate and predetermined pressure, wherein a stasis isachieved that is at or below the closure pressure of the well; b.maintaining the well at the stasis for a predetermined period of time;c. wherein, existing fractures are opened during the stasis; and, d.whereby the total production of hydrocarbons from the well is increased,compared to a first total product for the well prior to restimulation,by at least about 10%; e. wherein the stasis is maintained for about 30minutes to about 3 hours.
 4. A method of increasing a total productionof hydrocarbons from an existing well in a formation, over apredetermined period of time, the method comprising: a. pumping arestimulation fluid into the well at a predetermined flow rate andpredetermined pressure, wherein a stasis is achieved that is at or belowthe closure pressure of the well; b. maintaining the well at the stasisfor a predetermined period of time; c. wherein, existing fractures areopened during the stasis; and, d. whereby the total production ofhydrocarbons from the well is increased, compared to a first totalproduct for the well prior to restimulation, by at least about 10%; e.wherein the stasis is maintained for less than about 3 hours.
 5. Amethod of increasing a total production of hydrocarbons from an existingwell in a formation, over a predetermined period of time, the methodcomprising: a. pumping a restimulation fluid into the well at apredetermined flow rate and predetermined pressure, wherein a stasis isachieved that is at or below the closure pressure of the well; b.maintaining the well at the stasis for a predetermined period of time;c. wherein, existing fractures are opened during the stasis; and, d.whereby the total production of hydrocarbons from the well is increased,compared to a first total product for the well prior to restimulation,by at least about 10%; e. wherein the stasis is maintained form about 15minutes to about 2 hours.
 6. A method of stimulating a well havingexisting fractures, wherein the existing fractures comprise induced,naturally occurring or both fractures, and a production rate ofhydrocarbons, by repressurization, the method comprising: a. pumping arepressurization fluid into the well, thereby establishing andmaintaining a stasis that is at or below the closure pressure of thewell, wherein the stasis is maintained for a period of time comprising15 minutes to 2 hours; b. wherein at the stasis existing fractures areopened and pore surface are wetted with the repressurization fluid; and,c. whereby, the production rate of the well is increased.